Make Fermi Energy Optional for FHI-aims

[tpurcell90]

Summary

Make the Fermi energy an optional output because it is not always reported by FHI-aims.

Checklist

Work-in-progress pull requests are encouraged, but please put [WIP] in the pull request title.

Before a pull request can be merged, the following items must be checked:

• [x] Code is in the standard Python style. The easiest way to handle this is to run the following in the correct sequence on your local machine. Start with running ruff and ruff format on your new code. This will automatically reformat your code to PEP8 conventions and fix many linting issues.
• [x] Doc strings have been added in the Numpy docstring format. Run ruff on your code.
• [x] Type annotations are highly encouraged. Run mypy to type check your code.
• [x] Tests have been added for any new functionality or bug fixes.
• [x] All linting and tests pass.

Note that the CI system will run all the above checks. But it will be much more efficient if you already fix most errors prior to submitting the PR. It is highly recommended that you use the pre-commit hook provided in the repository. Simply run pre-commit install and a check will be run prior to allowing commits.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 76.90%. Comparing base (29a5731) to head (b29f038). Report is 10 commits behind head on main.

:exclamation: Current head b29f038 differs from pull request most recent head 74f1c4e. Consider uploading reports for the commit 74f1c4e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #793      +/-   ##
==========================================
+ Coverage   74.94%   76.90%   +1.95%     
==========================================
  Files         136      122      -14     
  Lines       10513     9110    -1403     
  Branches     1643     1430     -213     
==========================================
- Hits         7879     7006     -873     
+ Misses       2143     1675     -468     
+ Partials      491      429      -62     

Files	Coverage Δ
src/atomate2/aims/schemas/calculation.py	71.42% <66.66%> (-0.35%)	:arrow_down:

... and 30 files with indirect coverage changes

[JaGeo]

@tpurcell90 can you check again? Something does not seem to work!

[tpurcell90]

Sorry I thought this was done already it should be fixed now